The present invention relates generally to a level for determining an angular relationship between a line of interest, typically on a surface, and the horizontal. More particularly, the present invention relates to a level utilizing a weight, and alternatively a buoy, to bias an indicator in a position that represents the vertical, which position is calibrated relative to a housing for enabling determination of angular deviations of the line with respect to a horizontal plane.
Levels are used extensively in a variety of fields, particularly many related to construction. They enable an ascertainment of whether a line or a planar surface is horizontal when the apparatus is positioned on the line or surface. To determine whether a surface is horizontal, the angular deviations of lines on that surface are determined and appropriately combined using trigonometric calculations to determine a representation of the angular deviations of the plane of the surface from the horizontal. Levels typically have a longitudinal dimension which is positioned in operation to linearly correspond with the line of interest.
Perhaps the most common of previous levels has been the bubble level, also known as the "spirit level". This type of level consists essentially of an encased, liquid-filled tube containing an air bubble that moves to a center window when the instrument is set on a horizontal line. Their use is generally limited to determining whether a line is approximately close (within a small margin of error) to the horizontal. Such bubble levels are simple, generally accurate, and inexpensive; however, their accuracy is subject to error, and their use to determine the precise angular deviation from the horizontal is difficult, usually requiring triangulation to do so. Because of the shape of a bubble, the position of the bubble must be determined by the position of its perimeters which are curved lines. This determination is typically achieved by comparing the alignment of the longitudinal edges of the bubble with lines marked or etched on the window of the bubble level. When the bubble level is on an ideally horizontal surface, the line or lines that indicate a horizontal position should be tangential with the perimeter of the bubble. This tangential alignment, itself, allows room for some error, especially when considering the difficulties in viewing the edge of a bubble due to capillary effects between the liquid and the window. Even slight capillary effects cause the perimeters of the bubble to appear larger in width, and accuracy is diminished accordingly.
Furthermore, other errors may be encountered with bubble levels since a bubble level is typically calibrated with two linear markings which, when the level is on a horizontal surface, are each tangential to the bubble. While the distance between the two markings is constant, the size of the bubble must remain constant as well in order to avoid approximation. Practically, the precise volume of gas, as well as the shape of the bubble, must be maintained as constant. Each of these constants, however, are effected by several factors; for instance, an increase in temperature not only alters the shape of the bubble by increasing the pressure therein, but also increases the solubility of the gas within the liquid, tending to cause a decrease in the volume of the gas in the bubble. Thus, factors including temperature changes may add to errors in the use of bubble levels.
On the other hand, some apparatuses do not require bubbles to indicate the vertical, but rather utilize weights to determine a plumb and, thus, eliminate the problems associated with bubble levels. A common example of such an apparatus is the pendulum, which may be utilized for defining a plumb (a line perpendicular to the horizontal plane). Employment of such pendulums to determine whether the surface is horizontal, however, presents difficulties to one who is using the pendulum. This is particularly true when the pendulum is made in a compact size since the individual reading the pendulum is often positioned above the line of interest and looking down upon the pendulum from above. While the movement of the pendulum is at its lower end, an end which typically comprises a large, bulky mass, a user of a pendulum as a level encounters difficulties in reading the pendulum from above.
A rigid pendulum having an indicator propending diametrically opposite the pendulum's point of suspension would eliminate the previously mentioned problems of bubble levels while also providing an accurate indicator which can be gauged at the upper portion of the pendulum. This guaging at the upper portion enables the reading of the pendulum from above. Such devices are termed weight-biased levels for the purposes of this discussion. They have a single, rigid pendulum, rotating about a central axis with a weight to bias its indicator in the vertical direction; however, while such pendulums have been typically formed by casting or machining, it has been extremely costly and difficult to produce such a rigid rotating pendulum which is perfectly symmetrical. Such perfect symmetry is necessary in order to propend the vertical indicator in a position which represents the true vertical position. This impossibility is primarily due to the inevitable fluctuations in density of the materials used to produce such pendulums, including common fluctuations caused by voids and other inclusions in the material.
As a result, the production of accurate weight-biased levels has been inhibited by the necessity to machine away portions of the weight from one symmetrical side to the other, in an itterative fashion, until the pendulum indicates a representation of the true vertical position. Such itterative machining is costly, time consuming and still has accuracy limits depending on the machining instruments.
Thus, it is an object of the present invention to provide a weight-biased level apparatus which includes means for enabling the indication of a component representing the true vertical direction and which does not require machining in order to balance the rotating pendulum.
Furthermore, while such rotating pendulums must be suspended about virtually frictionless bearings in order to eliminate error in indicating the vertical, weight-biased levels tend to rotate about their rotational axis back and forth, in an oscillatory manner, for substantial period of time before finally coming to a rest. Thus, it is another object of the present invention to provide a weight-biased level apparatus which is highly accurate and which comes to rest indicating the vertical in as short a time as possible.
Accordingly, it can be seen by one of ordinary skill in the art, in light of the foregoing and subsequent discussions, that there is a need to overcome these and other problems relating to level apparatuses. It is also toward such objectives that the present invention is directed.